1. Field of the Invention
The present invention relates to color correction suitable for matching ambient light.
2. Related Background Art
Recent technical improvements on image processing apparatus has resulted in low cost color image processing apparatus. Color images can therefore be used widely, not only in a specific field such as designs with computer graphics but also in general offices.
One problem under such circumstances is that colors of two color images (displayed image and printed image) displayed on a monitor such as a CRT and printed out on a recording medium with a printer or the like, are different in color. Attention is now being paid to color management systems in order to solve this problem.
With color management systems, color images to be formed by a plurality of devices are represented by a common color space in order to avoid different colors on the devices. These systems for making the colors of images on the devices have the same color, rely on the fundamental concept that two colors represented by the same coordinate values in the color space are seen as the same color by the human eye. For current color management systems, a method has been proposed by which a difference in color between devices is corrected by using XYZ tristimulus values as the color space.
Conventional image observation environments will be described with reference with FIG. 17 which show an image 202 and a printed matter 201 on a monitor 203. Reference numeral 204 represents ambient light when an image is observed, the ambient light being, for example, radiation from a fluorescent lamp. Reference numeral 205 represents a screen installed so as to avoid any influence of radiation from the monitor 203 upon observation of the printed matter 201. Under such environment, photometry (measurement of chromaticity coordinates) is executed relative to the printed matter 201 and the image 202 on the monitor 203. The ideal state in color management systems is coincidence of photometric values of the printed matter 201 and the image 202.
However, under the environment such as shown in FIG. 17, ambient light 204 may change in various ways and the printed matter 201 and the image 202 on the monitor 203 are not always observed under the same environment. Even if color matching in the color space is obtained through color management under one kind of ambient light 204, the printed matter 201 and the image 202 are observed to be different colors under another kind of ambient light 204.
The invention has been made under the above circumstances. It is an object of the present invention to realize color matching irrespective of a change in the observation environment.
According to one aspect of the invention, an image processing apparatus is provided which comprises: means for determining an adaptation ratio of a reference white color value to at least two white color values; means for calculating a reference white color value in accordance with the determined adaptation ratio; and means for converting an image signal in accordance with the calculated reference white color value.
According to another aspect of the invention, an image processing apparatus for reading an original image with input means and outputting the original image from output means, is provided which comprises: first conversion means for converting an image signal read with the input means into a first image signal of a common color space; means for detecting ambient light information; means for storing white color information of the output means; means for determining adaptation ratios of reference white color information to white color information of the output means and the ambient light information; means for calculating the reference white color information in accordance with the adaptation ratios determined by the determining means; second conversion means for converting the first image signal into a second image signal in the common color space in accordance with the reference white color information; and third conversion means for converting the second image signal into a third image signal capable of being output from the output means.
The present invention solves the above problem and aims at realizing the same observed color of a subject and its image even if the background color becomes different.
According to another aspect of the invention, an image processing method for converting a color signal by using a reference white color signal is provided wherein the reference white color signal is determined in accordance with background color.
According to another aspect of the invention, an image processing method for converting a color signal. by using a reference white color signal calculated from adaptation ratios for two or more white colors, is provided wherein the adaptation ratio is calculated in accordance with background color.
The above and other objects, and features of the invention will become apparent from the following detailed description of embodiments when read in conjunction with the accompanying drawings.